1. Field of the Invention
This invention relates to a catalyst for olefin polymerization and a process for producing ethylene copolymers. More particularly, this invention relates to an olefin polymerization catalyst comprising a solid catalyst component exhibiting a very high activity per transition metal in gas phase polymerization process and slurry polymerization process, as well as to a process for producing ethylene copolymers having a narrow molecular weight distribution and a small content of low molecular weight component by the use of said catalyst. Further, this invention relates also to a process for producing ethylene copolymers having a high bulk density, a low fine powder content and a good flow property while controlling the particle shape of solid catalyst component quite excellently.
It is needless to say that a high catalyst activity (quantity of polymerization per unit quantity of catalyst), particularly a high activity per transition metal, is quite valuable industrially because it makes unnecessary the removal of catalyst residue from the polymer after polymerization and thereby simplifies the production process of polymer.
On the other hand, it is desirable to minimize the adhesion of polymer to polymerization reactor as possible because the adherent polymer makes various troubles on the operations and thereby lowers the efficiency of work. Thus, a high bulk density, a narrow particle size distribution and a good flow property of polymer powder are desirable from the viewpoint of stability and efficiency of operation. Further, molecular weight distribution and existence (or nonexistence) of low molecular weight component are factors governing transparency, impact resistance and blocking property of processed articles, and a process capable of producing an ethylene copolymer having a narrow molecular weight distribution and a small content of low molecular weight component is desirable.
2. Description of the Related Art
In the recent years, catalyst made of a transition metal compound supported on a carrier such as titanium tetrachloride and the like were developed (Belgian Patent Application No. 759,601, Japanese Patent Kokoku (Post-Exam Publn) No. Sho 47-46269, Japanese Patent Kokoku No. Sho 47-26,383, etc.). Although this type of catalysts are higher in polymerizing activity than prior catalysts, they are yet insufficient in the point of catalyst activity per transition metal.
On the other hand, as a catalyst system made from a solid product prepared by reducing a titanium compound with organomagnesium, the solid catalyst component composed of Grignard reagent and titanium tetrachloride or alkoxy-containing titanium halide (Japanese Patent Kokai (Laid-Open) No. Sho 46-4,391, Japanese Patent Kokoku No. Sho 47-40,959, Japanese Patent Kokoku No. Sho 50-30,102, etc.) and the solid catalyst component prepared by reacting Grignard reagent and alkoxy-containing titanium halide and treating the reaction product with titanium tetrachloride (Japanese Patent Kokoku No. Sho 57-24,361, Japanese Patent Kokai No. Sho 56-115,302, etc.) have been reported. However, these catalysts are yet insufficient in catalyst activity per transition metal and particle characteristics of solid catalyst component.
On the other hand, there have been disclosed a few catalyst components supported on porous inorganic carriers (Japanese Patent Kokai No. Sho 54-148,093, 56-24,409, 58-179,207, etc.). However, they are yet insufficient in the point of catalyst activity and adhesion to polymerization reactor.